The purpose of the proposed research will be to determine whether successive milestones in infants' vocal development indicating their ability to control different articulatory units (utterance, syllable, phoneme, and distinctive feature) are related to different types of handedness during the first two years of life. Three studies will be conducted in the regard: 1) A short-term longitudinal study will test whether the onset of cooing at 6 to 8 weeks of age is related to the waning of the tonic neck reflex and the emergence of both an asymmetry of grasp and differential manual swiping. 2) Longitudinal and cross-sectional designs will be used to test whether the beginning of repetitive babbling of similar syllables by 6 months of age is related to the emergence of unimanual handedness. Measures of electroencephalographic asymmetries will be used as a converging operation for the presence of hemispheric specialization in the cross-sectional study. 3) A cross-sectional study with 18 and 24 month-olds will test for the onset of a manual preference for bimanual alternating tapping and will provide preliminary evidence linking this preference to infants' ability to use distinctive features in their vocal production. In conjunction with past evidence for a developmental relation between infants' use of phonemes in speech and bimanual handedness toward the end of the first year of life, positive evidence in these studies would be consistent with the view that structural changes in infants' vocalizations for the control of different articulatory units reflect successive levels of hemispheric specialization for the control of the vocal apparatus during the first two years of life.